Portable hammer



Feb. 27, 1962 w` F. MITCHELL PORTABLE HAMMER Filed Feb. 5, 1959 3,022,838 PORTABLE HAMMER Y Wallace F. Mitchell, Arlington Heights, Ill., assigner to The Thor Power Tool Company, a corporation of Delaware Filed Feb. 5, 1959, Ser. No. 791,457 2 Claims. (Cl. 175-147) This invention relates to a portable hammer and moreV particularly to improvements in the construction of such hammers resulting in a reduction in recoil, however, the invention is not necessarily so limited.

An obejct of this invention is to provide a portable hammer having a free flying impact delivering piston.

Another object of this invention is to provide a portable hammer of improved low recoil construction.

Another object of this invention is to provide a percussion tool having a reciprocating impact delivering piston carrying a free floating mass eective to counteract recoil.

Still another object of this invention is to provide an improved reciprocating percussion tool utilizing a spring as an energizing means wherein the spring is carried in free flying movement by a driven piston.

Still another object of this invention is to provide, in a percussion tool, improved means for adjusting the intensity of the blow delivered by such tool.

A further object of this invention is to provide, in an impact delivering tool including a reciprocating piston for delivering an impact to a tool holding member, improved resilient mounting means for supporting the tool holding member in the path of the reciprocating piston.

Other objects and advantages reside in the construction of parts, the combination thereof the method of manufacture and the mode of operation, as will become more apparent from the following description.

In the drawing,

FIGURE l is a plan view with portions shown in section illustrating the portable hammer of this invention.

FIGURE 2 is a sectional view taken substantially along the line 2 2 of FIGURE l.

Referring to the drawing in detail, the portable hammer illustrated in FIGURE 1 includes an elongate cylindrical barrel rigidly secured to a housing l2. Integral with the housing 12 is a generally rectangular mounting plate 14 to which a motor housing 1S is secured by means of threaded screw elements 16. The housing 18 terminates in a pistol grip handle 20 and houses motive means subject to the control of a handle switch shown schematically at 2l. The motive means may be a motor which is electric, hydraulic, or pneumatic, or any other suitable source of power.

Mounted for sliding reciprocal movement within the barrel l0 is a substantially cylindrical piston 22. EX- tending into the rearward end of the piston 22, that is, the right end of the piston as viewed in FIGURE 1, is an axial boring 24 receiving a coiled compression spring 26. The spring 26 is confined in the boring by means of a free sliding cylindrical keeper 2S retained within the boring 24 by means of an expansion ring 3d. The keeper 28 is hollowed out and provided with air vents 32 which prevent compression of the air within the boring 24.

The opposite or forward end of the piston 22 terminates in a portion 34 of reduced diameter which telescopically receives a hollow hammer head 36. This head is anchored to the portion 34 by means of a transverse pin 38. Disposed within the interior of the hammer head is a free floating dense mass in the form of loose shot 4t) which may be steel, for example. The Steel shot 4l) lls about two-thirds of the interior of the hammer head.

Within the housing 12 the underside of the barrel 10 is cut away as illustrated at 42 in FIGURE 1. Projecting through this cut away portion is a cam follower roller 44 journalled upon a pin 46 projecting transversely into the piston 22. Partially enclosing the roller 44 is a sear member 48 which has substantially diametrically disposed downwardly projecting fingers 50d and 50b. These lingers partially straddle a shaft 52 disposed within the housing 12 in spaced parallel relation to the barrel 10. This shaft 52 is driven rotatably by the motive means in the housing 18 and receives bearing support in a portion 54.

Projecting from the periphery of the shaft 52 is a helical beveled cam ridge 56 which, upon rotation of the shaft 52- in the counterclockwise sense as viewed in FIGURE 2, engages the roller 44 to drive the piston 22 rearwardly, or to the right as viewed in FIGURE 1. The roller 44 has a complementary bevel. This rearward movement ofthe piston 22 brings the spring keeper 28 into engagement with a plunger or abutment 58 projecting axially from a cylindrical body 60 threadedly engaging the rearward end of the barrel l0. The extreme rearward end of the body 60 is knurled at 62 for convenient manual adjustment of the position of the plunger 58. Air vents 64. in the wall of the barrel 10 adjacent the body 60 prevent compression of air upon rearward movement of the piston 22. Y

The action of the plunger 58 upon engagement with the spring keeper 28 is such as to compress the spring 26. The extent to which the spring 26 is compressed depends upon the axial length of the cam ridge-56 and upon the position of the plunger 58. Since the plunger 58 is adjustable, the compression of the spring is adjustable.

Referring to FIGURE 2, it is there indicated that the shaft 52 is rotated in a counterclockwise direction. When the trailing edge 57 of the cam ridge 56 has moved counterclockwise past the roller 44 and past the finger- 50a, the piston 22 is disengaged from the cam ridge 56 and vfree to move forward. The finger 50a is beveled complementary to the cam ridge 56 to give a scar action as the trailing edge 57 of the cam ridge 56l clears the finger. ln other words, the finger 50a is designed to abruptly release the piston 22. In the embodiment illustrated, the cam ridge 56 travels angularly through about 240 of the periphery of the shaft 52 and the beveledA edge of the finger 56a is about 60" away from the center of the roller 44. Thus, the cam ridge 56 engages the roller 44 and/or the finger Sila throughout about 300 of rotation of the shaft 52. Movement of the piston 22 and the hammer head 36 toward the forward end of the barrel l0 takes place while` the shaft 52 rotates the remaining 60 of one revolution.

Positioned in the forward path of the piston 22 is a tool holder 66 terminating at its forward end with a socket 68 adapted to receive a tool bit and terminating at its rearward end with an anvil portion 67. Centrally 1ocated in the tool holder 66 is an annular groove 70 which receives a generally toroidal elastomeric body 72. In securing the tool holder to the barrel lil the anvil end is slid telescopically intothe forward end of the .barrel 10 and a retaining cap 74 is projected over they socket 68 to threadedly engage the forward end of thebarrel. As the cap 74 is positioned aboutthe tool holder, theA toroidal body 72, which is larger in diameter than the bore in the barrel 1i) is compressed into the groove 70.

It is apparent that the mounting for the tool holder is such that it may move both forwardly and rearwardly subjectto the restraining action of the toroidal body 72. To prevent escape of the tool holder 66, should the toroidal body 72 fail under repeated impact, the opening in the cap 74 which receives the socket 68 is 3,022,838? A A Y made smaller in diameter than the anvil portion 67. Thus, the tool holder can be removed only after the cap 74 has been removed. This construction also prevents shearing of the toroidal body by the anvil portion 67. To minimize damage to the body 72, the rearward wall ofthe groove 70 is tapered.

The tool holder 66 is located a distance from the plunger 58 which exceeds the overall length of the hammer head 36 and the piston 22. The design is preferably such that this condition prevails irrespective of adjustments in the p-lunger 58. 1n consequence of this construction, the hammer head 36, the piston 22, and the spring 26 carried thereby are always free flying in the barrel 10 when an impact is delivered to the tool holder.

Adjacent the anvil portion 67, the barrel 1.0 is provided with air vents 76 which obviate compression of air in the barrel 10 as the hammer head 36 is driven toward the tool holder. f

The operation of the device is as follows: With a desired tool bit positioned in the socket 68, the tool bit is positioned in contact with the surface which is to receive impacts delivered by the portable hammer. Preferably the operator applies slight pressure so that the tool holder 66 tends to move inwardly of the barrel 10. With the `tool bit in position, the switch 21 is actuated to start the motive means within the housing 18. This rotates the shaft 52 and the cam ridge 56, which drives the piston 22 rearwardly compressing the spring 26. As the trailing edge 57 of the cam ridge 56 clears the tinger 50a, the piston 22 is abruptly released and impelled forwardly by the spring 26. Before the hammer head 36 strikes the tool holder, the piston and the hammer head are free ying within the barrel 10. Due to the inertia of the mass 40, it is at rest in therearward end of the hammer head 36 during the forward flight thereof.

When the hammer head strikes the tool holder, its weight exclusive of the steel shot 40, the weight of the piston, and the weight of the spring 26 all contribute to the impact delivered. Assuming that the operator is exerting at least slight pressure so that the tool bit firmly engages the work, the impact is transmitted directly to the work and only little impact, if any, is transmitted through the toroidal body 72 to the housing. In general, the harder the operator presses the tool bit against the work, the smaller the impact which will be transmitted to the housing structure.

Immediately after impact, the tool holder 66 and the piston 22 commence a recoil action and, in the absence of a counteracting force, the recoil action of the tool holder 66 will be transmitted through the toroidal body 72 to the housing. As this recoil action commences, however, the mass of steel shot 40'in the hammer head, moving forward -inder its own momentum, delivers a delayed blow to the end of the hammer head. This blow opposes the recoil of the tool holder 66, thus reducing recoil transmitted to the housing. Following this, the beveled cam ridge S reengages the cam follower roller 44 to initiate a new operating cycle.

In the use of this device, it is to be noted that the pressure which the operator exerts on the tool bit may cause the tool holder to move inwardly of the barrel 10, compressing the toroidal body 72. This decreases the distance between the tool holder and the plunger 58, however, the spacing between the tool holder and the plungerV 58 is preferably large enough that the piston 22 and the hammer head will remain free flying notwithstanding this movementot` the tool holder. Thus, the pressure which the operator exerts, while it may shorten the overall stroke of the piston, will not limit the extension of the spring 26 and therefore will not lessen the impact delivered. Rather,` the operator pressure is additive to the impact delivered.

upon release Although the preferred embodiment of the device has been described, it will be understood that within the purview of this invention various changes may be made in the form, details, proportion and arrangement of parts, the combination thereof and mode of operation, which generally stated consist in a device capable of carrying out the objects set forth, as disclosed and defined in the appended claims.

Having thus described my invention, I claim:

1. In an impact delivering device including a housing having an elongate bore therein, a cylindrical piston mounted for sliding movement in said bore, a tool holding attachment, means supporting said tool holding attachment in one end of said bore, and motive means for reciprocating the piston so as to deliver repeated impacts to said tool holding attachment, the improvement wherein said tool holding attachment projects partly out of said bore, and the means supporting the tool holding attachment includes Van elastomeric toroidal body, said tool holding attachment having an annular groove therein receiving said toroidal body, said toroidal body having an outer diameter exceeding the diameter of said bore and being positioned adjacent one end of said bore, and a cap member projecting telescopically over the outwardly projecting portion of said tool holding attachment to threadedly engage said housing, said 'cap member having an opening therein concentric with said bore through which the outwardly projecting end of said tool holding attachment projects, the diameter of said opening being less than the diameter of said bore.

2. An impact delivering device comprising, in combination, a housing having an elongate cavity therein, means providing an abutment at the rearward end of said cavity, a tool holder supported at the forward end of said cavity, a piston and a compression spring carried thereby mounted for sliding reciprocal movement in said cavity, said piston having an elongate boring extending into the rearward end thereof receiving said compression spring, a keeper for said spring slidably mounted in said boring and biased rearwardly thereof by said spring, and means providing a retainer in said boring for limiting the rearward movement of the keeper, said housing supporting said abutment and said tool holder at a distance one from the other which exceeds the overall length of the piston together with the spring carried thereby, and drive means for actuating said piston rearwardly towards said abutment and for releasing said piston at a predetermined rearward position in said cavity, said keeper being aligned with said abutment such that upon the piston being driven rearwardly by said drive means the abutment actuates the keeper to compress the spring, the compressed spring of said piston propelling the piston in unison therewith forwardly to the tool holder to deliver an impact thereto.

References Cited in the file of this patent UNITED STATES PATENTS 423,620 Menendez Mar. 18, 1890 1,053,744 Philips Feb. 18, 1913 1,123,547 Jost Jan. S, 1915 1,798,082 Grutzbach Mar. 24, 1931 1,803,307 Wodack Apr. 28, 1931 2,020,018 Coates Nov. 5, 1935 2,185,471 Mall Jan. 2, 1940 Y2,260,070 Wilhide Oct. 21, 1941 2,342,601 Pyle Feb. 22, 1944 2,501,542 Sheldonv Mar. 2l, 1950 2,604,914 Kahlen July 29, 1952 2,685,274 4Liddicoat Aug. 3, 1954 2,737,216 Kenerson Mar. 6, 1956 FOREIGN PATENTS 805,268 Germany May 10, i 

